The hermetically sealed motor compressor comprises, in general, a motor compressor unit including a motor assembly mounted with a frame and a sealed housing within which the motor compressor is supported by means of a plurality of coil springs each having one end connected with the frame and the other end connected with the interior of the housing. An inlet coupling is fixed to the wall of the sealed casing for introducing a low-temperature refrigerant gas into the sealed casing, and a discharge outlet coupling is fixed to the wall of the casing which is coupled to the discharge muffler through a tubular conduit. And, as the discharge gas is relatively hot due to the compression process, it is generally desirable to minimize heat transfer to the suction gas so as to maintain a high volumetric efficiency.
The volumetric efficiency of the compressor is the actual volume of gas pumped divided by the calculated cylinder volume, and several factors affect the volumetric efficiency. One factor which affects the actual volumetric efficiency, under the condition that the high side pressure and low side pressure of the compressor are maintained constant, is the temperature of the gas to be suctioned to the cylinder. The density of high temperature gas is low so that, when the cylinder is filled by the high temperature gas, very small amount, by weight, is represented, and reduces the actual pumping capacity.
A variety of attempts have been made to meet the foregoing requirement. According to certain proposals, the outlet of the suction coupling extending through and secured to the wall of the sealed casing is located as closely as possible to the suction port of suction muffler, or joined to the suction port so that the refrigerant gas will be introduced from the suction coupling into the suction muffler to minimize heat conduction in the sealed casing (see U.S. Pat. No. 4,242,056) with another prior art the suction muffler and discharge muffler are disposed separately from the cylinder, to prevent the refrigerant gas from being heated in the suction process to the cylinder (see U.S. Pat. Nos. 3,411,705, 3,480,206 and 3,600,110). These arrangements are not so effective for attaining high volumetric efficiency because the suction gas led into suction chamber is warmed by the heated discharge gas. In the previous compressor, a cylinder head is mounted on the top of the valve plate and contains the suction chamber and the discharge chamber, which are separated by means of the cross wall. As the discharge chamber is warmed to a relatively higher temperature by the hot refrigerant gas discharged out of the cylinder due to the refrigerant compression process, and the low temperature refrigerant gas introduced from the suction coupling into the suction muffler and led into an suction chamber is warmed and draw into the cylinder, the conventional cylinder head is less effective for volumetric efficiency and therefore the compressor can not attain the high efficiency.
The refrigerant gas as it is compressed in the cylinder is discharged through the discharge chamber in the cylinder head into the discharge muffler. The discharge muffler is generally mounted on the cylinder head attached in covering relation to an end face of the cylinder (see U.S. Pat. No. 3,698,840). Where the sealed casing is spherical in shape for better noise suppresion, an upper end of the cylinder head tends to interfere with an inner wall surface of the sealed casing, a disadvantage which can only be eliminated by increasing the size of the sealed casing for providing a desired hermetically sealed motor compressor.